The present invention relates to compositions suitable for golf ball constructions, and to golf balls which employ those compositions.
Modern golf balls typically employ ionomeric resins as cover materials. lonomeric resins, as a result of their toughness, durability, and wide range of hardness values have become materials of choice for golf ball covers over traditional rubbers. lonomeric resins generally comprise an xcex1-olefin and an xcex1, xcex2 ethylenically unsaturated mono- or dicarboxylic acid neutralized with metal ions to the extent desired. Olefins which have been employed to prepare ionomeric resins include ethylene, propylene, butene-i and the like. Unsaturated carboxylic acids which have been employed to prepare ionomeric resins include acrylic, methacrylic, ethacrylic, o-chloroacrylic, crotonic, maleic, fumaric, itaconic and the like. lonomeric resins include copolymers of ethylene with acrylic acid such as those sold by Exxon Corporation under the trademark xe2x80x9cIOTEKxe2x80x9d, as well as copolymers of ethylene with methacrylic acid such as those sold by E.I. DuPont Nemours and Company under the trademark xe2x80x9cSURLYNxe2x80x9d. In some instances, a softening comonomer such as an acrylate ester has been included such that the ionomeric copolymer is an ionomeric terpolymer. Although various compositions have been employed to provide golf balls of varying playability characteristics, a need continues for compositions and covers which can be employed to provide golf balls which exhibit good playability and durability.
There are no commercially available golf balls which are generally known to contain nylon. Nylon alone would be too brittle for use in a golf ball cover. When efforts have been made in other fields to blend nylon with softer materials some degree of incompatibility often has resulted, rendering the blends susceptible to cracking and premature failure. U.S. Pat. No. 4,690,981, the contents of which are incorporated herein by reference, shows soft terpolymer ionomers of ethylene/unsaturated carboxylic acid/softening comonomer which are useful in injection-molded items such as ski boots, ice skate shells, as coatings for fabrics, and as a replacement for balata in golf balls. The unsaturated carboxylic acid may be, for example, acrylic acid and methacrylic acid. The softening comonomer is, for example, an alkyl acrylate such as n-butyl acrylate. The ""981 patent briefly mentions that the ionomers can be blended with other materials such as nylon, polypropylene, propylene-ethylene copolymers, linear polyethylene, and ethylene/unsaturated carboxylic acid copolymers. However, there is no indication that blends can be used for golf balls.
An object of the invention is to provide a highly durable golf ball.
Another object of the invention is to provide a golf ball with a cover layer containing reduced quantities of ionomer.
A further object of the invention is to provide a golf ball having a high coefficient of restitution.
Another object of the invention is to provide a durable golf ball with a low spin rate.
Yet another object of the invention is to provide a golf ball having a hard cover layer which is resistant to cracking.
Another object of the invention is to provide a method of making a golf ball with a cover layer of the type described above.
Other objects of the invention will be in part obvious and in part pointed out more in detail hereinafter.
The invention in a preferred form is a golf ball having a cover layer with a resin composition comprising a combination of a polyamide component and an ionomeric component, the content of the polyamide component being at least 23 wt % of the resin composition, the golf ball having a coefficient of restitution of at least 0.750. The polyamide component preferably includes at least one member selected from the group consisting of a polyamide homopolymer and a polyamide copolymer. In one preferred form of the invention, at least a portion of the polyamide component and at least a portion of the ionomeric component are part of the same copolymer. In another form of the invention, the polyamide component is present in a mixture with the ionomeric component. The combination preferably has 23-85 wt % polyamide component and at least 15-77 wt % ionomeric component.
In one particularly preferred form of the invention, the combination further includes an ester component. The ester component can be, for example, an olefin ester component. At least a portion of each of the polyamide component, ionomeric component and ester component preferably are part of the same copolymer. The composition of this embodiment optionally further comprises a carboxylic acid-containing copolymer which includes at least one member selected from the group consisting of ionomeric copolymers and non-ionomeric terpolymers and which is mixed with the copolymer of polyamide, ionomer and ester components.
In another particularly preferred form of the invention, the ionomeric component includes an acrylate ester. The polyamide component preferably is in a mixture with the ionomeric component. In yet another embodiment of the invention, the combination of a polyamide component and ionomeric component is mixed with a non-polyamide-containing copolymer.
Some examples of the invention include a graft copolymer or blend of a polyamide homopolymer with one or both of an ionomeric terpolymer and an ionomeric copolymer with two types of monomers. Preferred polyamides for use according to the invention are polymers of caprolactam such as polyepsiloncaprolactam (nylon 6), polyhexamethyleneadipamide (nylon 66), and copolymers of nylon 6 and nylon 66. The ionomeric component of the invention preferably is a copolymer formed from an xcex1-olefin having 2 to 8 carbon atoms and an acid which is selected from the group consisting of xcex1, xcex2-ethylenically unsaturated mono- or dicarboxylic acids and is neutralized with cations which include at least one member selected from the group consisting of zinc, lithium, sodium, manganese, calcium, chromium, nickel, aluminum, potassium, barium, tin, copper, and magnesium ions. Preferred cations are zinc, sodium and lithium, and combinations thereof. In one preferred embodiment, the copolymer is further formed from an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms. The golf ball preferably has a Durability Rating of at least 2.
Another preferred form of the invention is a golf ball having a cover layer with a composition comprising a graft copolymer of (1) at least one of a polyamide homopolymer and a polyamide copolymer and (2) a first ionomeric copolymer which is formed from an xcex1-olefin and a carboxylic acid. The golf ball has a Durability Rating of at least 2. The cover layer has a Shore D hardness of at least 30.
Yet another preferred form of the invention is a golf ball having a cover layer with a composition comprising a nylon backbone with ionomer grafted thereto, the golf ball having a coefficient of restitution of at least 0.750.
Another preferred form of the invention is a golf ball having a cover layer with a composition comprising a combination of a polyamide and a non-ionomeric acid copolymer which is formed from an xcex1-olefin, an ester, and a carboxylic acid. The golf ball preferably has a Durability Rating of at least 2.
A further preferred form of the invention is a golf ball having a cover layer comprising at least 10 wt % of a graft copolymer of polyepsiloncaprolactam and ionomer, the graft copolymer having a yield tensile strength of about 54 MPa (ASTM D-638), a flexural modulus of about 1585 MPa (ASTM D-790), and a drop weight impact at xe2x88x9240xc2x0 F. of about 200 J (ASTM D-3029). In a particularly preferred form of the invention, the cover layer comprises at least 80 wt % of the graft copolymer.
Yet another preferred form of the invention is a method of making a golf ball. The method comprises steps of obtaining a golf ball core, and forming a cover layer over the core, the cover layer having a resin composition comprising a combination of a polyamide component and an ionomeric component, the content of the polyamide component being at least 23 wt % of the resin composition, the golf ball having a coefficient of restitution of at least 0.750.
The invention comprises the several steps in the relation of one or more such steps with respect to each of the others, and the article possessing the features, properties and the relation of elements exemplified in the following detailed disclosure.